This invention relates to a semiconductor pattern mask having features to minimize aberrations. More particularly, this invention relates to a semiconductor pattern mask having sub-resolution features to reduce the sensitivity of the pattern to aberrations in the optics of the pattern imaging system.
Semiconductor devices are typically manufactured using photolithographic techniques. The circuit elements or structures to be formed are drawn on a mask. The mask can be a xe2x80x9cdark field layoutxe2x80x9d in which the circuit elements are represented by light-transmissive areas on a nontransmissive (or less transmissive) background, or a xe2x80x9cclear field layoutxe2x80x9d in which the circuit elements are represented by nontransmissive (or less transmissive) areas on a transmissive background.
A silicon substrate, suitably doped, is provided with a photosensitive coating or xe2x80x9cphotoresist.xe2x80x9d The photosensitive coating is exposed to light through the mask using an optical system, and is then processed to develop the circuit elements on the silicon substrate. The process is repeated for multiple layers of silicon and metallization (using a different mask for each layer) until the desired circuit has been formed.
The optical elements in the optical system used to expose the photosensitive surface through the mask may be imperfect. For example, lenses in that system may be manufactured with one of several optical aberrations.
One such aberration, known as three-leaf aberration, may cause distortion of the imaging of the mask features onto the photosensitive surface, resulting in corresponding distortions in the final semiconductor device.
It would be desirable to be able to provide a way to eliminate the sensitivity of semiconductor pattern mask to three-leaf aberration.
Preferably, in accordance with the present invention, a semiconductor pattern mask includes first features intended to form structures in the semiconductor end product, and second features that differ from such first features in a way that breaks up three-fold symmetry in the pattern, and may or may not form structures in the semiconductor end product. The latter features may be of different transmissivity than the former features, which results in breaking up the three-fold symmetry. In one embodiment, the differing transmissivity is a result of a difference in the size of the features, with additional features being smaller than the features intended to form structures. The smaller features are not intended to form structures, but still are large enough to affect the pattern of transmitted light. In another embodiment, certain features may transmit light at a relative phase different than that of the light transmitted by other features. The certain features may be of substantially the same size as the other features, both of which being intended to form structures in the semiconductor end product, or the certain features may be smaller than the other features, and not intended to form structures in the semiconductor end product.